Combustion can be used for regenerating reactors utilized for cyclic, high temperature chemistry, e.g., regenerative reactors. Typically, regenerative reactor cycles are either symmetric (reaction chemistry is the same as regeneration chemistry) or asymmetric (reaction chemistry and regeneration chemistry are different).
One class of asymmetric regenerative reactors, e.g., those utilized for pyrolysis, comprises first and second zones, with each zone comprising at least one regenerative bed. The reactor is heated (or regenerated) in an exothermic oxidation step, e.g., by conducting fuel and oxidant to a mixing-distribution zone located between the first and second zones, mixing and distributing the fuel and oxidant in the mixing-distribution zone, combusting the fuel and oxidant, and then conducting the combustion products through the second zone and away from the reactor. During the pyrolysis step, a pyrolysis feed is conducted through the second zone and then through the first zone, thereby pyrolysing the pyrolysis feed and conveying heat from the second zone to the first zone. Some regenerative reactors deliver fuel and/or oxidant directly to the mixing-distribution zone without having those streams pass through the first or second zones. Prior art references disclose introducing fuel and/or oxidant via nozzles, distributors, or burners that penetrate the reactor system using means generally perpendicular to the reaction flow direction and usually through the reactor vessel side wall. For example, during the exothermic step in a conventional Wulff cracking furnace, air flows axially through the regenerative bodies, and fuel is introduced via nozzles that penetrate the side of the furnace, to combine with air (combusting and releasing heat) in an open zone between regenerative bodies.
One feature of a regenerative reactor is to execute reactions at high efficiency by recuperating product heat directly into feeds. Introducing fuel or oxidant radially via nozzles, distributors, or burners external to the reactor is disadvantageous because the regenerative reactor system is not utilized to preheat that reactant stream. In other words, bypassing some fraction of the fuel and/or oxidant around the regenerative reactor system reduces the reactor system's efficiency.
Attempts have been made to introduce fuel and/or oxidant to a location at or near the middle of the regenerative reactor via conduits that are positioned axially within one or more of the regenerative beds. For example, U.S. Pat. No. 4,240,805 discloses using pipes that are positioned axially within a regenerative bed to carry oxidant (air) to locations near the middle of the regenerative flow path. This conveys heat toward the reforming zone. More recently, U.S. Pat. No. 7,815,873 discloses providing fuel and oxidant, via substantially parallel flow paths within the first zone, to a mixer-distributor located in a mixing-distributing zone. The mixing-distributing zone is located between the first and second regenerative zones, and the mixer-distributor comprises convergence and divergence zones to improve the reactor's thermal efficiency.
Further improvements are desired.